active range of waypoints, PSS FMC

[sanyok]

waypoints over 100nt. miles apart seem unable to be picked up and followed by the FMC, or is it me doing something wrong?

Flying over water, with fiew waypoints across, FMC is useless.
Do I have to add more waypoints into the flightplan? (20 / 40 of them), which doesn't make sense to me, there has to be something else I don't know of.

Also while on PSS topic, flying A340: I have an Alt. Hold problem: it goes up and down in cruise, with VS ranging up to 1700fpm (-1700 to + 1700). Climb was as difficult, VS going from -200 to +4,000. Nothing like that was experienced with A320 family.

As fuel is burned, the fluctuation in VS becomes reduced (-/+200fpm), but, I cannot begin a flight with an ampty tanks, can I?

[boeboeke]

There is no FMC in an Airbus. The system is called FMGS, tne computers for this system FMGC and the device to enter and read data is the MCDU.
The FMGS is not flying the plane towards the radio signal of the waypoints, but towards the geographical locations, so it doesn't matter if you pick them up or not. Did you enter the right waypoints into the F.PLN page of the MCDU? Are you in NAV MODE?
I can't explain the ALT problem, might be a PSS problem. Are you in MANAGED ALT MODE ? Is the AP on ?

[sanyok]

yes everything was on, all was managed by FMGC (what does "G" stand for?)

I used it with POSky's A330/340 models, possibly that's the reason for the problem. OK with that, now... The flightplan had two waypoints over the ocean (each at the edge of europran cost and north american cost). As I passed the last waypoint of european cost (bound to NY), the vector line on ND towards the next waypoint (on north american cost) suddenly vanished. The flightplan was still active, but autopilot didn't know where to fly the plane. I set heading by my self, the north american waypoint showed up on ND when about 80 miles out, with vectoring to the next waypoint.

OK I don't wanna confuse you and go insane, better yet, let me ask you this:
How do FMCs/FMGCs work/what is the core in it: the GPS or INS?

[boeboeke]

Didn't you have a DISCONTINUITY line between the two waypoints in your flightplan? If any of these lines, remove them.
The waypoint showed up on your ND when about 80 miles out, because you had, probably, your ND at the 80NM setting.
FMGS stands for Flight Management Guidance System
FMGC stands for Flight Management Guidance Computer
MCDU stands for Multifunctional Control Display Unit.

When talking about entering a flightplan or any other data you should always refer to the MCDU. The FMGS is always working, even if you did not enter a flightplan. The FMGS drives the AP in NAV MODE, as well as in HDG/TRK MODE. The FMGS makes sure, that none of the commands you give (stick, throttle, etc..) will result in an unsafe behaviour of the plane. Even if you push the stick fully to the right or the left, the plane will never bank more than 67°.
Do not forget that in an Airbus, the Fly By Wire technology is used. There is no direct connection between the stick, throttles, pedals and the ailerons, rudder, engines,... The pilot only inputs his command, the computer calculates and executes.

An Airbus uses both INS and GPS. INS is the primary system. The accuracy of the navigation is computed by the FMGC by comparing both results.